The freeze-fracture technique will be used to determine the effects of deafferentation and axotomy on the postsynaptic specializations of the principal neuron in the anterior anteroventral cochlear nucleus of the guinea pig. The most significant result of this research will be an understanding of the potential of the synaptic membrane to respond to changes in its environment. This understanding is important for understanding the mechanisms involved in establishing and maintaining synaptic contacts. In addition, information will be gained concerning the roles that the postsynaptic and presynaptic neuron play in maintaining the postsynaptic members specializations. Finally, the freeze-fracture technique will contribute new information concerning the response of the CNS neuron to pathological conditions. This research will also be significant in terms of its contribution to the understanding of the auditory system. It will include an intensive thin section and freeze-fracture study of a single synapse of the spiral ganglion cells in the anterior AVCN. The geometric arrangement of the active zones and distribution of the postsynaptic membrane specializations are distinctive. By studying the particle distribution on the postsynaptic membrane under different experimental conditions insight will be gained as to the relationship of the different particle specializations to synaptic function at the primary auditory synapse. Future work resulting from this study will focus on comparing the events that occur on the postsynaptic membrane during degeneration with that which occurs during the development of the synaptic contacts. Evidence on the development of receptors in the neuromuscular junction and of synaptic specializations during the synaptogenesis in tissue culture indicate that such comparisons would be significant. The characteristic size and arrangements of the end bulb of Held in the anterior AVCN make it easy to identify in thin sections and freeze-fracture replicas. These same features would make this synapse a good model for future studies on synaptic development with the freeze-fracture.